This　paper　presents　an　experimental　investigation　into　the　failure　behavior　of　a　large-scale　assembled　spread　foundation　for　wind　turbines,　subjected　to　combined　loading　of　bending　moment,　shear　force,　and　vertical　force.　Seven　load　cases　are　established　to　explore　the　failure　mode,　cracking　pattern,　and　nonlinearity　development　of　the　test　model.　The　results　indicate　that,　under　the　ultimate　limit　state　(ULS),　failure　of　the　test　model　is　governed　by　soil　damage,　directly　leading　to　a　decline　in　the　structural　load-bearing　capacity.　The　cantilever　root　in　the　uplift　region　is　the　main　cracking　area　for　the　joints,　and　the　tilt　rate　of　the　foundation　far　exceeds　the　code　requirements　under　ULS.　Notably,　through　innovative　calculation　of　local　internal　forces　at　the　joints,　the　specific　areas　with　higher　stress　levels　are　identified,　accounting　for　the　observed　primary　joint　cracking　areas　and　facilitating　reasonable　joint　design　to　prevent　failure.　Besides,　it　is　found　that　the　lower　limit　of　tension　control　stress　as　per　the　code　is　insufficient　to　meet　the　crack　width　limits,　thereby　highlighting　the　significance　of　adequate　prestress　in　crack　control.　Furthermore,　a　linear　decreasing　trend　of　maximum　crack　widths　at　key　load-bearing　joints　with　an　increase　in　the　foundation＇s　axial　load　ratio　is　also　disclosed.　Finally,　a　prediction　formula　for　nonlinear　critical　loads　resulting　from　soil-structure　interaction　is　established　to　prevent　soil　degradation　under　cyclic　loading.　©　2025　Elsevier　Ltd